Tools to manufacture abrasive articles

ABSTRACT

The present invention provides master and production tools and method for making these tools. The master tool includes a plurality of three-dimensional shapes upraised from a major surface of the master tool. Each of the shapes is defined by a distinct and discernible boundary including specific dimensions, wherein not all said three-dimensional shapes are identical. The master tool of the present invention can be used to form a production tool containing a plurality of three-dimensional-shaped cavities. The production tool can be used in the manufacture of abrasive articles to shape an abrasive slurry into an array of three-dimensional shaped abrasive composites.

RELATED APPLICATIONS

[0001] This application is a division of application Ser. No. 09/259,488(filed Feb. 26, 1999) now pending, which application is a division ofapplication Ser. No. 08/940,267 (filed Sep. 29, 1997) now pending, whichis a continuation of application Ser. No. 08/450,814 (filed May 25,1995), now abandoned, which is a division of application Ser. No.08/120,300 (filed Sep. 13, 1993), now abandoned.

BACKGROUND OF THE INVENTION

[0002] The invention relates to tools used to manufacture an abrasivearticle having a sheet-like structure having a major surface havingdeployed thereon a plurality of abrasive composites having definedshapes, wherein the shapes are not all identical.

[0003] In general, abrasive articles employ a plurality of abrasiveparticles which are bonded together as a unitary structure (e.g., agrinding wheel) or bonded separately to a common backing (e.g., a coatedabrasive article). While these types of abrasive articles have beenutilized to abrade and finish workpieces for many years, problems remainin the field.

[0004] For instance, one persistent problem confronting the abrasiveindustry arises from the generally inverse relationship associatedbetween the cut rate (i.e., the amount of workpiece removed for a giventime interval) and the finish that is imparted by the abrasive articleon the workpiece surface. That is, it is difficult to design an abrasivearticle that affords a relatively high rate of cut while concomitantlyimparting a relatively fine surface finish on the workpiece beingabraded. This explains the presence of a wide range of abrasive productsin the market using coarse grit (i.e., relatively large particle size ofabrasive particles) to fine grit (i.e., relatively small particle sizeof abrasive particles). The use of these differently grit-sized abrasiveproducts in a separate and sequential manner can provide some measure ofsuccess in ultimately achieving both a high cut and a fine finish, butthe practice can be cumbersome and time consuming. Naturally, a singleabrasive article which simultaneously would provide both high cut rateand fine finish would be more convenient and highly desired in theindustry.

[0005] In addition to these goals, it has also been desired in theabrasive industry to provide an abrasive article which imparts aconsistent surface finish in the workpiece while lessening or preventingscribing and/or chatter. Scribing refers to the occurrence of pronouncedunwanted grooves in the workpiece surface which results in an increasein surface roughness units (Ra). Ra is the arithmetic average of thescratch depth. Typically, the grooves, when they occur, extend in thesurface of the workpiece in a direction tracking the relative motion ofthe abrasive article vis-a-vis the workpiece surface. On the other hand,chatter means an undesirable repetitive pattern created on the surfaceof a workpiece, usually at regular spaced intervals at a directionperpendicular to the direction of belt movement.

[0006] While various attempts have been made to create new and improvedabrasive products, no complete solution to the problems noted above havebeen presented. While the following list of references describe avariety of abrasive products none is known to provide a completelysatisfactory result to these problems.

[0007] More specifically, U.S. Pat. No. 2,115,897 (Wooddell et al.)teaches an abrasive article having a backing and attached thereto by anadhesive are a plurality of blocks of bonded abrasive material. Thesebonded abrasive blocks can be adhesively secured to the backing in aspecified pattern.

[0008] U.S. Pat. No. 2,242,877 (Albertson) teaches a method of making acompressed abrasive disc. The method involves embedding abrasiveparticles in a binder layer that is coated on a fibrous backing. Then, amold die is used to impart a molded pattern or contour into thethickness of binder and particle layer under heat and pressure to form acompressed abrasive disc. The molded surface of the abrasive disc has aspecified working surface pattern which is the inverse of the profile ofthe molding die.

[0009] U.S. Pat. No. 2,755,607 (Haywood) teaches a coated abrasive inwhich there are land and groove abrasive portions, which can form, forexample, an overall rectlinear or serpentine pattern. An adhesive coatis applied to the front surface of a backing and this adhesive coat isthen combed to create peaks and valleys to pattern the surface of theadhesive coat. Haywood discloses that each of the lands and groovesformed in the adhesive coat by such a combing procedure preferably havethe same width and thickness, but that they may be varied. Next theabrasive grains are distributed uniformly in the lands and grooves ofthe previously patterned adhesive coat followed by solidification of theadhesive coat. The abrasive particles used in Haywood are individualgrains which are not used in slurry form with other grains in a binder.Therefore, the individual abrasive grains have irregular non-preciseshapes.

[0010] U.S. Pat. No. 3,048,482 (Hurst) discloses an abrasive articlecomprising a backing, a bond system and abrasive granules that aresecured to the backing by the bond system. The abrasive granules are acomposite of abrasive grains and a binder which is separate from thebond system. The abrasive granules are three-dimensional and arepreferably pyramidal in shape. To make this abrasive article, theabrasive granules are first made via a molding process. Next, a backingis placed in a mold, followed by the bond system and the abrasivegranules. The mold has patternized cavities therein which results in theabrasive granules having a specified pattern on the backing.

[0011] U.S. Pat. No. 3,605,349 (Anthon) pertains to a lapping typeabrasive article. The binder and the abrasive grain are mixed togetherand then sprayed onto the backing through a grid. The presence of thegrid results in a patterned abrasive coating.

[0012] Great Britain Patent Application No. 2,094,824 (Moore) pertainsto a patterned lapping film. The abrasive slurry is prepared and theslurry is applied through a mask to form discrete islands. Next, theresin or binder is cured. The mask can be a silk screen, stencil, wire,or a mesh.

[0013] U.S. Pat. No. 4,644,703 (Kaczmarek et al.) concerns a lappingabrasive article comprising a backing and an abrasive coating adhered tothe backing. The abrasive coating further comprises a suspension oflapping size abrasive grains and a binder cured by free radicalpolymerization. The abrasive coating can be shaped into a pattern by arotogravure roll.

[0014] U.S. Pat. No. 4,773,920 (Chasman et al.) concerns a lappingabrasive article comprising a backing and an abrasive coating adhered tothe backing. The abrasive coating comprises a suspension of lapping sizeabrasive grains and a binder cured by free radical polymerization. Theabrasive coating can be shaped into a pattern by a rotogravure roll.

[0015] U.S. Pat. No. 4,930,266 (Calhoun et al.) teaches a patternedabrasive sheeting in which the abrasive granules are strongly bonded andlie substantially in a plane at a predetermined lateral spacing. In thisinvention the abrasive granules are applied via a impingement techniqueso that each granule is essentially individually applied to the abrasivebacking. This results in an abrasive sheeting having a preciselycontrolled spacing of the abrasive granules.

[0016] U.S. Pat. No. 5,014,468 (Ravipati et al.) pertains to a lappingfilm intended for ophthalmic applications. The lapping film comprises apatterned surface coating of abrasive grains dispersed in a radiationcured adhesive binder. The patterned surface coating has a plurality ofdiscrete raised three-dimensional formations having widths whichdiminish in the direction away from the backing. To make the patternedsurface, an abrasive slurry is applied to a rotogravure roll to providea shapes surface which is then removed from the roll surface and thenthe radiation curable resin is cured.

[0017] U.S. Pat. No. 5,015,266 (Yamamoto) pertains to an abrasive sheetby uniformly coating an abrasive adhesive slurry over an embossed sheet.The resulting abrasive coating has high and low abrasive portions formedby the surface tension of the slurry, corresponding to theirregularities of the base sheet.

[0018] U.S. Pat. No. 5,107,626 (Mucci) teaches a method of providing apatterned surface on a substrate by abrading with a coated abrasivecontaining a plurality of precisely-shaped abrasive composites. Theabrasive composites are in a non-random array and the abrasivecomposites comprise a plurality of abrasive grains dispersed in abinder.

[0019] U.S. Pat. No. 5,152,917 (Pieper et al.) discloses a coatedabrasive article that provides both a relatively high rate of cut and arelatively fine surface finish on the workpiece surface. The structuredabrasive of Pieper et al. involves precisely-shaped abrasive compositesthat are bonded to a backing in a regular nonrandom pattern. Theconsistency of the profile of the abrasive composites provided by theabrasive structure of Pieper et al., among other things, helps provide aconsistent surface finish in the worked surface.

[0020] Japanese Patent Application No. S63-235942 published Mar. 23,1990 teaches a method of a making a lapping film having a specifiedpattern. An abrasive slurry is coated into a network of indentations ina tool. A backing is then applied over the tool and the binder in theabrasive slurry is cured. Next, the resulting coated abrasive is removedfrom the tool. The binder can be cured by radiation energy or thermalenergy.

[0021] Japanese Patent Application No. JP 4-159084 published Jun. 2,1992 teaches a method of making a lapping tape. An abrasive slurrycomprising abrasive grains and an electron beam curable resin is appliedto the surface of an intaglio roll or indentation plate having a networkof indentations. Then, the abrasive slurry is exposed to an electronbeam which cures the binder and the resulting lapping tape is removedfrom the roll.

[0022] U.S. Pat. No. 5,437,754 (Calhoun), which is commonly assigned tothe owner of the present application, teaches a method of making anabrasive article. An abrasive slurry is coated into recesses of anembossed substrate. The resulting construction is laminated to a backingand the binder in the abrasive slurry is cured. The embossed substrateis removed and the abrasive slurry adheres to the backing.

[0023] U.S. Pat. No. 5,219,462 (Bruxvoort et al.) teaches a method formaking an abrasive article. An abrasive slurry is coated substantiallyonly into the recesses of an embossed backing. The abrasive slurrycomprises a binder, abrasive grains and an expanding agent. Aftercoating, the binder is cured and the expanding agent is activated. Thiscauses the slurry to expand above the surface of the embossed backing.

[0024] U.S. Pat. No. 5,435,816 (Spurgeon et al.), which is commonlyassigned to the owner of the present application, teaches a method ofmaking an abrasive article. In one aspect of this patent application, anabrasive slurry is coated into recesses of an embossed substrate.Radiation energy is transmitted through the embossed substrate and intothe abrasive slurry to cure the binder.

[0025] U.S. Pat. No. 5,913,716 (Mucci et al.), which is commonlyassigned to the owner of the present application, teaches a method ofpolishing a workpiece with a structured abrasive. The structuredabrasive comprises a plurality of precisely-shaped abrasive compositesbonded to a backing. During polishing, the structured abrasiveoscillates.

[0026] The use of variable pitch sawing teeth has been disclosed as acutting edge for a hack saw blade, such as mentioned in a tradeadvertisement distributed by Lenox Co. and entitled “Lenox Hackmaster VVari-Tooth Power Hack Saw Blades”, to provide balanced cutting actionand quiet performance. This hack saw blade design is described as usefulto saw metal bar stock, ganged workpieces, or work with holes, slots orinterruptions. This hack saw blade design is not specifically disclosedas adaptable for frictional abrasion applications between two rubbingsurfaces including a complex three-dimensional working surface, nor doesthe LENOX publication disclose the wherewithal therefor.

[0027] Although some of the abrasive articles made according to theaforementioned patents, viz. Pieper et al., might provide an abrasivearticle yielding both high rate of cut and relatively fine finish, ithas been observed that scribing can occur in surfaces worked by someprior art abrasive articles when the abrasive articles are used. Forinstance, many abrasive articles have directional limitations insofar ashow the articles are to be oriented relative to the work surface to bereduced, i.e., some articles cannot be used omnidirectionally. If usedimproperly by accident or neglect, e.g., if such an abrasive article isnot properly aligned with the surface to be worked by the operator,these abrasive articles, among other things, can cause scribing in theworked surface.

[0028] Therefore, it can be understood that the abrasive industry wouldhighly value a versatile high-cut rate, fine finish abrasive articlewhich is more resistant to inadvertent scribing and more adaptable to awider range of abrasive conditions.

SUMMARY OF THE INVENTION

[0029] The present invention provides master and production tools whichare useful for manufacturing a unique abrasive article. The master toolincludes a plurality of three-dimensional shapes upraised from a majorsurface. Each of the shapes is defined by a distinct and discernibleboundary including specific dimensions, wherein not all thethree-dimensional shapes are identical. The master tool of the presentinvention can be used to form a production tool containing a pluralityof three-dimensional-shaped cavities. The production tool can be used inthe manufacture of abrasive articles to shape an abrasive slurry into anarray of three-dimensional shaped abrasive composites.

[0030] The invention provides a master tool for providing a productiontool for making an abrasive article comprising a backing having a majorsurface having deployed in fixed position thereon first and secondthree-dimensional abrasive composites, each of the composites comprisingabrasive particles dispersed in a binder and having a shape defined by asubstantially distinct and discernible boundary which includessubstantially specific dimensions, wherein the first abrasive compositehas a shape having specific first dimensions and the second abrasivecomposite has a second shape having second specific dimensions, whereeach of the abrasive composites has a boundary defined by at least fourplanar surfaces wherein adjacent planar surfaces of one composite meetat an edge to define an angle of intersection therebetween, wherein atleast one angle of intersection of the first abrasive composite isdifferent from all of the angles of intersection of the secondcomposite. The master tool comprises a structure having a major surfacehaving a plurality of adjacent three-dimensional shapes projectingtherefrom, wherein each three-dimensional shape is defined by asubstantially distinct and discernible boundary which includessubstantially specific dimensions, wherein a first three-dimensionalshape has a first shape having specific first dimensions and a secondthree-dimensional shape has a second shape having second specificdimensions, wherein each of the three-dimensional shapes has a boundarydefined by at least four planar surfaces wherein adjacent planarsurfaces of one three-dimensional shape meet at an edge to define anangle of intersection therebetween, wherein at least one angle ofintersection of the first three-dimensional shape is different from allangles of intersection of the second three-dimensional shape.

[0031] The master tool may be made by a method which comprises the stepsof:

[0032] (1) determining angles corresponding to facing right and leftplanar surfaces of adjacent three-dimensional shapes wherein each of theangles has a value as measured between its planar surface and a planewhich extends in a normal direction to the major surface and contains anedge of the planar surface in contact with the major surface, by thefollowing substeps:

[0033] (i) selecting an angle value between, but not including, 0° and90° to establish a first right half angle of a first right planarsurface of a first right-side three-dimensional shape with a randomnumber generating means capable of randomly selecting an angle valuebetween, but not including, 0° and 90°;

[0034] (ii) selecting an angle value between, but not including, 0° and90° with said random number generating means to establish a first lefthalf angle for a first left planar surface of a first left-sidethree-dimensional shape facing the first right planar surface of thefirst right-side three-dimensional shape;

[0035] (iii) proceeding along a first direction extending linearlywithin the first imaginary plane to a second left planar surface of asecond left-side three-dimensional shape located adjacent the firstleft-side three-dimensional shape and using the random number generatingmeans to select a value between, but not including, 0° and 90° toestablish a second left planar angle for the second left planar surface;

[0036] (iv) using the random number generating means to select a valuebetween, but not including, 0° and 90° for a second right planar surfaceof a second right-side three-dimensional shape facing said second leftplanar surface;

[0037] (v) proceeding along the first direction to a third right-sidethree-dimensional shape located adjacent said second right-sidethree-dimensional shape;

[0038] (vi) repeating substeps (i), (ii), (iii), (iv), and (v), in thatsequence, at least once;

[0039] (2) repeating step (1) except that the angles are determined forleft and right planar surfaces of adjacent three-dimensional shapesdeployed in two adjacent rows in a second direction extending linearlywithin said first imaginary plane, wherein said first and seconddirections intersect;

[0040] (3) using means to determine, for a given width of said surfaceof said master, locations of grooves required to be cut by a cuttingmeans to form a series of intersecting grooves defining a plurality ofprecise three-dimensional shapes having said angles calculated by steps(1) and (2); and

[0041] (4) providing a cutting means to cut grooves in the surface ofthe master in correspondence to the angles calculated by steps (1) and(2) and the groove locations determined by step (3) to form a series ofintersecting grooves which define a plurality of three-dimensionalshapes upraised from the surface, each of the shapes being defined by adistinct and discernible boundary including specific dimensions, whereinnot all said three-dimensional shapes are identical.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is an end sectional view representing one embodiment of anabrasive article made with a production tool which was made with themaster tool of this invention.

[0043]FIG. 2 is an end sectional view representing another embodiment ofan abrasive article which may be made by use of the production tool madewith the master tool of this invention.

[0044]FIG. 3 is a side schematic view showing an apparatus for makingthe abrasive articles depicted in FIGS. 1 and 2.

[0045]FIG. 4 is a side schematic view showing an alternate apparatus formaking the abrasive articles depicted in FIGS. 1 and 2.

[0046]FIG. 5 is a Scanning Electron Microscope (SEM) photomicrographtaken at 45× of the top surface of an abrasive article having 355micrometer high pyramidal-shaped abrasive composites of varyingdimension.

[0047]FIG. 6 is a SEM photomicrograph taken at 25× of the top surface ofa polypropylene production tool of the present invention having about355 micrometer deep pyramidal-shaped cavities of varying dimensions.

[0048]FIG. 7 is a plane view in schematic of a production tool which canbe made with the master tool of the invention.

[0049]FIG. 8 is a schematic plane view of the topography of an abrasivearticle having pyramidal shapes for all the abrasive composites, whereinadjacent shapes have the same height but different side angles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The abrasive article of the invention exhibits a high rate of cutwhile imparting a relatively level, fine surface finish on the workpiecebeing abraded and does not readily scribe the workpiece. While notdesiring to be bound to any theory at this time, it is hypothesized thatan array of abrasive composites having perfect pitch, i.e., an array ofabrasive composites that are all identical in dimensions, may generate avibrational resonance, whereby the working abrasive article surface mayreach a resonant vibration state which can cause surface finishproblems, known as chatter marks. In the present invention, it isbelieved that the variation in the dimensions between adjacentprecisely-shaped abrasive composites disrupts and/or prevents suchvibrational resonance from developing to thus provide a high cut-rate,fine finish with decreased chatter incidence in addition to decreasedscribing.

[0051] For purposes of this invention, the expression“precisely-shaped”, or the like, as used herein in describing theabrasive composites that are formed and cured on the surface of theproduction tool, refers to abrasive composites having a shape that hasbeen formed by curing the curable binder of a flowable mixture ofabrasive particles and curable binder while the mixture is both beingborne on a backing and filling a cavity on the surface of a productiontool. Such a “precisely-shaped” abrasive composite would thus haveprecisely the same shape as that of the cavity, although other shapescould be made by forming the composites on the tool surface and curingthem off the tool surface. Further, the precise shape of the abrasivecomposite is defined by relatively smooth-surfaced sides that arebounded and joined by well-defined sharp edges having distinct edgelengths with distinct endpoints defined by the intersections of thevarious sides with the proviso that at least one of said abrasivecomposites has at least one dimension which is different from that of anadjacent abrasive composite or composites.

[0052] For purposes of this invention, the term “boundary”, as usedherein to define the abrasive composites, means the exposed surfaces andedges of each abrasive composite that delimit and define the actualthree-dimensional shape of each abrasive composite. These distinct anddiscernible boundaries are readily visible and clear when across-section of the abrasive article of the invention is examined undera microscope such as a scanning electron microscope. The distinct anddiscernible boundaries of each abrasive composite form thecross-sectional outlines and contours of the precise shapes of thepresent invention. These boundaries separate and distinguish oneabrasive composite from another even when the abrasive composites abutteach other along a common border at their bases. By comparison, in anabrasive composite that does not have a precise shape, the boundariesand edges are not definitive, e.g., where the abrasive composite sagsbefore completion of its curing.

[0053] For purposes of this invention, the term “dimension”, as used inconnection with defining the abrasive composites, means a measure ofspatial extent such as an edge length of a side surface (inclusive ofthe base) of the shape associated with an abrasive composite or,alternatively, the “dimension” can mean a measure of an angle ofinclination of a side surface extending from the backing. Therefore, forpurposes of this invention, a “dimension” that is “different” for twodifferent abrasive composites, means an edge length or an angle ofintersection made at the meeting edge of two planar surfaces of a shapeof a first abrasive composite that is nowhere duplicated in value by anyof the edge lengths or angles of intersections defining the shape of asecond abrasive composite in the array. These first and second abrasivecomposites can be adjacent in a preferred embodiment.

[0054] For purposes of this invention, the terminology “geometricalshape” means a basic category of three-dimensional regular geometricalshape, such as cubic, pyramidal, pyrismatic, conical, cylindrical,truncated pyramidal, truncated conical and the like.

[0055] For purposes of this invention, the terminology “adjacentcomposite” or “adjacent composites”, or the like, as used herein, meansat least two neighboring composites which lack any intervening abrasivecomposite structure located on a direct line therebetween.

[0056] Referring to FIG. 1 for illustrative purposes, the side view ofthe abrasive article 10 shows a backing 11 having a pair of oppositeside edges 19 (one shown), a machine direction axis (not shown) wouldextend parallel to the direction of said side edges 19 for purposes ofthis illustration, and a plurality of abrasive composites 12 fixed to atleast the top surface 16 of the backing. The abrasive composites 12comprise a plurality of abrasive particles 13 dispersed in the binder14. Each abrasive composite has a discernible precise shape. It ispreferred that the abrasive particles do not protrude beyond the planarsurface planes 15 of the shape before the coated abrasive article is putinto service. As the coated abrasive article is being used to abrade asurface, the composite breaks down revealing unused abrasive particles.

[0057] In one aspect of the invention, viz., where the abrasivecomposites are spaced-apart at constant pitch (constant peak-to-peakdistance from centers of adjacent abrasive composites), the “adjacentcomposite” will involve one nearest neighboring composite or multiplenearest neighboring composites equidistantly spaced from the abrasivecomposite which has the different dimension thereto. However, in anotheraspect of the invention, if the abrasive composites are spaced at avaried pitch, then it is possible, in that instance, for the “adjacentcomposite” to involve an abrasive composite which is not necessarily theclosest composite as spaced from the abrasive composite having thedifferent dimension thereto, as long as no intervening abrasivestructure is located on a direct line therebetween.

[0058] Backing

[0059] A backing can be conveniently used in this invention to provide asurface for deploying the abrasive composites thereon, wherein such abacking has a front and back surface and can be any conventionalabrasive backing. Examples of such include polymeric film, primedpolymeric film, cloth, paper, vulcanized fiber, nonwovens, andcombinations thereof. The backing optionally may be a reinforcedthermoplastic backing as described in the assignee's co-pending U.S.Pat. No. 5,316,812 (Stout et al.) or an endless belt as described in theassignee's U.S. Pat. No. 5,573,619 (Benedict et al.). The backing mayalso contain a treatment or treatments to seal the backing and/or modifysome physical properties of the backing. These treatments are well knownin the art.

[0060] The backing may also have an attachment means on its back surfaceto secure the resulting coated abrasive to a support pad or back-up pad.This attachment means can be a pressure sensitive adhesive or a loopfabric for a hook and loop attachment. Alternatively, there may be aintermeshing attachment system as described in the U.S. Pat. No.5,201,101 (Rouser et al.) incorporated herein by reference.

[0061] The back side of the abrasive article may also contain a slipresistant or frictional coating. An example of such a coating includecompositions containing an inorganic particulate (e.g., calciumcarbonate or quartz) dispersed in an adhesive. An antistatic coatingcomprising materials such as carbon black or vanadium oxide also may beincluded in the abrasive article, if desired.

[0062] Abrasive Composite

[0063] a. Abrasive Particles

[0064] The abrasive particles typically have a particle size rangingfrom about 0.1 to 1500 micrometers, usually between about 0.1 to 400micrometers, preferably between 0.1 to 100 micrometers and morepreferably between 0.1 to 50 micrometers. It is preferred that theabrasive particles have a Mohs' hardness of at least about 8, morepreferably above 9. Examples of such abrasive particles include fusedaluminum oxide (which includes brown aluminum oxide, heat treatedaluminum oxide, and white aluminum oxide), ceramic aluminum oxide, greensilicon carbide, silicon carbide, chromia, alumina zirconia, diamond,iron oxide, ceria, cubic boron nitride, boron carbide, garnet, andcombinations thereof.

[0065] The term abrasive particles also encompasses when single abrasiveparticles are bonded together to form an abrasive agglomerate. Abrasiveagglomerates are further described in U.S. Pat. No. 4,311,489(Kressner); U.S. Pat. No. 4,652,275 (Bloecher et al.) and U.S. Pat. No.4,799,939 (Bloecher et al.) incorporated herein by reference.

[0066] It is also within the scope of this invention to have a surfacecoating on the abrasive particles. The surface coating may have manydifferent functions. In some instances the surface coatings increaseadhesion to the binder, alter the abrading characteristics of theabrasive particle, and the like. Examples of surface coatings includecoupling agents, halide salts, metal oxides including silica, refractorymetal nitrides, refractory metal carbides, and the like.

[0067] In the abrasive composite there may also be diluent particles.The particle size of these diluent particles may be on the same order ofmagnitude as the abrasive particles. Examples of such diluent particlesinclude gypsum, marble, limestone, flint, silica, glass bubbles, glassbeads, aluminum silicate, and the like.

[0068] b. Binder

[0069] The abrasive particles are dispersed in an organic binder to formthe abrasive composite. The organic binder can be a thermoplasticbinder, however, it is preferably a thermosetting binder. The binder isformed from a binder precursor. During the manufacture of the abrasivearticle, the thermosetting binder precursor is exposed to an energysource which aids in the initiation of the polymerization or curingprocess. Examples of energy sources include thermal energy and radiationenergy which includes electron beam, ultraviolet light, and visiblelight. After this polymerization process, the binder precursor isconverted into a solidified binder. Alternatively for a thermoplasticbinder precursor, during the manufacture of the abrasive article thethermoplastic binder precursor is cooled to a degree that results insolidification of the binder precursor. Upon solidification of thebinder precursor, the abrasive composite is formed.

[0070] The binder in the abrasive composite is generally alsoresponsible for adhering the abrasive composite to the front surface ofthe backing. However, it some instances there may be an additionaladhesive layer between the front surface of the backing and the abrasivecomposite.

[0071] There are two main classes of thermosetting resins, condensationcurable and addition polymerized resins. The preferred binder precursorsare addition polymerized resin because they are readily cured byexposure to radiation energy. Addition polymerized resins can polymerizethrough a cationic mechanism or a free radical mechanism. Depending uponthe energy source that is utilized and the binder precursor chemistry, acuring agent, initiator, or catalyst is sometimes preferred to helpinitiate the polymerization.

[0072] Examples of typical binders precursors include phenolic resins,urea-formaldehyde resins, melamine formaldehyde resins, acrylatedurethanes, acrylated epoxies, ethylenically unsaturated compounds,aminoplast derivatives having pendant unsaturated carbonyl groups,isocyanurate derivatives having at least one pendant acrylate group,isocyanate derivatives having at least one pendant acrylate group, vinylethers, epoxy resins, and mixtures and combinations thereof. The termacrylate encompasses acrylates and methacrylates.

[0073] Phenolic resins are widely used in abrasive article bindersbecause of their thermal properties, availability, and cost. There aretwo types of phenolic resins, resole and novolac. Resole phenolic resinshave a molar ratio of formaldehyde to phenol greater than or equal toone to one, typically between 1.5:1.0 to 3.0:1.0. Novolac resins have amolar ratio of formaldehyde to phenol of less than one to one. Examplesof commercially available phenolic resins include those known by thetradenames DUREZ and VARCUM from Occidental Chemicals Corp.; RESINOXfrom Monsanto; AEROFENE from Ashland Chemical Co. and AEROTAP fromAshland Chemical Co.

[0074] Acrylated urethanes are diacrylate esters of hydroxy terminatedNCO extended polyesters or polyethers. Examples of commerciallyavailable acrylated urethanes include UVITHANE 782, available fromMorton Thiokol Chemical, and CMD 66001, CMD 8400, and CMD 8805,available from Radcure Specialties.

[0075] Acrylated epoxies are diacrylate esters of epoxy resins, such asthe diacrylate esters of bisphenol A epoxy resin. Examples ofcommercially available acrylated epoxies include CMD 3500, CMD 3600, andCMD 3700, available from Radcure Specialities.

[0076] Ethylenically unsaturated resins include both monomeric andpolymeric compounds that contain atoms of carbon, hydrogen, and oxygen,and optionally, nitrogen and the halogens oxygen or nitrogen atoms orboth are generally present in ether, ester, urethane, amide, and ureagroups. Ethylenically unsaturated compounds preferably have a molecularweight of less than about 4,000 and are preferably esters made from thereaction of compounds containing aliphatic monohydroxy groups oraliphatic polyhydroxy groups and unsaturated carboxylic acids, such asacrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, maleic acid, and the like. Representative examples ofacrylate resins include methyl methacrylate, ethyl methacrylate styrene,divinylbenzene, vinyl toluene, ethylene glycol diacrylate, ethyleneglycol methacrylate, hexanediol diacrylate, triethylene glycoldiacrylate, trimethylolpropane triacrylate, glycerol triacrylate,pentaerythritol triacrylate, pentaerythritol methacrylate,pentaerythritol tetraacrylate and pentaerythritol tetraacrylate. Otherethylenically unsaturated resins include monoallyl, polyallyl, andpolymethallyl esters and amides of carboxylic acids, such as diallylphthalate, diallyl adipate, and N,N-diallyladipamide. Still othernitrogen containing compounds include tris(2-acryloyloxyethyl)isocyanurate, 1,3,5-tri(2-methyacryloxyethyl)-s-triazine,acrylamide, methylacrylamide, N-methylacrylamide,N,N-dimethylacrylamide, N-vinylpyrrolidone, and N-vinylpiperidone.

[0077] The aminoplast resins have at least one pendant alpha,beta-unsaturated carbonyl group per molecule or oligomer. Theseunsaturated carbonyl groups can be acrylate, methacrylate, or acrylamidetype groups. Examples of such materials includeN-hydroxymethyl)-acrylamide, N,N′-oxydimethylenebisacrylamide, ortho andpara acrylamidomethylated phenol, acrylamidomethylated phenolic novolac,and combinations thereof. These materials are further described in U.S.Pat. No. 4,903,440 (Larson et al.) and U.S. Pat. No. 5,236,472 (Kirk etal.), both incorporated herein by reference.

[0078] Isocyanurate derivatives having at least one pendant acrylategroup and isocyanate derivatives having at least one pendant acrylategroup are further described in U.S. Pat. No. 4,652,274 (Boettcher etal.) incorporated herein after by reference. The preferred isocyanuratematerial is a triacrylate of tris(hydroxy ethyl) isocyanurate.

[0079] Epoxy resins have an oxirane and are polymerized by the ringopening. Such epoxide resins include monomeric epoxy resins andoligomeric epoxy resins. Examples of some preferred epoxy resins include2,2-bis[4-(2,3-epoxypropoxy)-phenyl propane] (diglycidyl ether ofbisphenol A) and commercially available materials under the tradedesignation EPON 828, EPON 1004, and EPON 100 IF available from ShellChemical Co., DER-331, DER-332, and DER-334 available from Dow ChemicalCo. Other suitable epoxy resins include glycidyl ethers of phenolformaldehyde novolac (e.g., DEN-431 and DEN-428 available from DowChemical Co.).

[0080] The epoxy resins of the invention can polymerize via a cationicmechanism with the addition of an appropriate cationic curing agent.Cationic curing agents generate an acid source to initiate thepolymerization of an epoxy resin. These cationic curing agents caninclude a salt having an onium cation and a halogen containing a complexanion of a metal or metalloid. Other cationic curing agents include asalt having an organometallic complex cation and a halogen containingcomplex anion of a metal or metalloid which are further described inU.S. Pat. No. 4,751,138 (Tumey et al.) incorporated herein by reference(column 6 line 65 to column 9 line 45). Another example is anorganometallic salt and an onium salt is described in U.S. Pat. No.4,985,340 (Palazzotto) (column 4 line 65 to column 14 line 50); EuropeanPatent Applications 306,161 and 306,162, all incorporated herein byreference. Still other cationic curing agents include an ionic salt ofan organometallic complex in which the metal is selected from theelements of Periodic Group IVB, VB, VIB, VIIB and VIIIB which isdescribed in European Patent Applications 109,851 incorporated herein byreference.

[0081] Regarding free radical curable resins, in some instances it ispreferred that the abrasive slurry further comprise a free radicalcuring agent. However in the case of an electron beam energy source, thecuring agent is not always required because the electron beam itselfgenerates free radicals.

[0082] Examples of free radical thermal initiators include peroxides,e.g., benzoyl peroxide, azo compounds, benzophenones, and quinones. Foreither ultraviolet or visible light energy source, this curing agent issometimes referred to as a photoinitiator. Examples of initiators, thatwhen exposed to ultraviolet light generate a free radical source,include but are not limited to those selected from the group consistingof organic peroxides, azo compounds, quinones, benzophenones, nitrosocompounds, acryl halides, hydrozones, mercapto compounds, pyryliumcompounds, triacrylimidazoles, bisimidazoles, chloroalkytriazines,benzoin ethers, benzil ketals, thioxanthones, and acetophenonederivatives, and mixtures thereof Examples of initiators that whenexposed to visible radiation generate a free radical source, can befound in U.S. Pat. No. 4,735,632 (Oxman et al.), entitled CoatedAbrasive Binder containing Ternary Photoinitiator System incorporatedherein by reference. The preferred initiator for use with Visible lightis IRGACURE 369 commercially available from Ciba Geigy Corporation.

[0083] The weight ratios between the abrasive particles and binder canrange between 5 to 95 parts abrasive particles to 5 to 95 parts binder;more typically, 50 to 90 parts abrasive particles and 10 to 50 partsbinder.

[0084] c. Additives

[0085] The abrasive slurry can further comprise optional additives, suchas, for example, fillers (including grinding aids), fibers, lubricants,wetting agents, thixotropic materials, surfactants, pigments, dyes,antistatic agents, coupling agents, plasticizers, and suspending agents.The amounts of these materials are selected to provide the propertiesdesired. The use of these can affect the erodability of the abrasivecomposite. In some instances an additive is purposely added to make theabrasive composite more erodable, thereby expelling dulled abrasiveparticles and exposing new abrasive particles.

[0086] Examples of useful fillers for this invention include: metalcarbonates (such as calcium carbonate {such as chalk, calcite, marl,travertine, marble and limestone}, calcium magnesium carbonate, sodiumcarbonate, magnesium carbonate), silica {such as quartz, glass beads,glass bubbles and glass fibers} silicates {such as talc, clays,montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate,sodium aluminosilicate, sodium silicate}, metal sulfates {such ascalcium sulfate, barium sulfate, sodium sulfate, aluminum sodiumsulfate, aluminum sulfate}, gypsum, vermiculite, wood flour, aluminumtrihydrate, carbon black, metal oxides {such as calcium oxide or lime,aluminum oxide, titanium oxide}, and metal sulfites {such as calciumsulfite}).

[0087] The term filler also encompasses materials that are known in theabrasive industry as grinding aids. A grinding aid is defined asparticulate material that the addition of which has a significant effecton the chemical and physical processes of abrading which results inimproved performance. Examples of chemical groups of grinding aidsinclude waxes, organic halide compounds, halide salts and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes liketetrachloronaphtalene, pentachloronaphthalene; and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroboate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, magnesiumchloride. Examples of metals include, tin, lead, bismuth, cobalt,antimony, cadmium, iron, and titanium. Other miscellaneous grinding aidsinclude sulfur, organic sulfur compounds, graphite, and metallicsulfides.

[0088] Examples of antistatic agents include graphite, carbon black,vanadium oxide, humectants, and the like. These antistatic agents aredisclosed in U.S. Pat. Nos. 5,061,294 (Harmer et al.); 5,137,542(Buchanan et al.), and 5,203,884 (Buchanan et al.) incorporated hereinby reference.

[0089] A coupling agent can provide an association bridge between thebinder precursor and the filler particles or abrasive particles.Examples of coupling agents include silanes, titanates, andzircoaluminates. The abrasive slurry preferably contains anywhere fromabout 0.01 to 3% by weight coupling agent.

[0090] An example of a suspending agent is an amorphous silica particlehaving a surface area less than 150 meters square/gram that iscommercially available from DeGussa Corp., under the trade name OX-50.

[0091] Abrasive Composite Shape

[0092] Each abrasive composite has a precise shape associated with it.The precise shape is delimited by a distinct and discernible boundary,these terms being defined hereinabove. These distinct and discernibleboundaries are readily visible and clear when a cross-section of theabrasive article of the invention is examined under a microscope such asa scanning electron microscope, e.g., as shown in FIG. 5. The distinctand discernible boundaries of each abrasive composite form the outlineor contour of the precise shapes of the present invention. Theseboundaries separate and distinguish one abrasive composite from anothereven when the abrasive composites abutt each other along a common borderat their bases.

[0093] In comparison, in an abrasive composite that does not have aprecise shape, the boundaries and edges are not definitive, e.g., wherethe abrasive composite sags before completion of its curing. Thus, theexpression “precisely-shaped”, or the like, as used herein in describingthe abrasive composites, also refers to abrasive composites having ashape that has been formed by curing the curable binder of a flowablemixture of abrasive particles and curable binder while the mixture isboth being borne on a backing and filling a cavity on the surface of aproduction tool. Such a precisely-shaped abrasive composite would thushave precisely the same shape as that of the cavity. These cavities in aproduction tool are depicted in FIG. 6.

[0094] A plurality of such composites provide three-dimensional shapesthat project outward from the surface of the backing in an inversepattern to that presented by the production tool. Each composite isdefined by a well-defined boundary or perimeter, the base portion of theboundary being the interface with the backing to which theprecisely-shaped composite is adhered. The remaining portion of theboundary is defined as the inverse shape of the cavity in the surface ofthe production tool in which the composite is cured. The entire outersurface of the composite is confined, either by the backing or by thecavity, during its formation. Suitable methods and techniques forforming precisely-shaped composites are disclosed in U.S. Pat. No.5,152,917 (Pieper et al.), which is incorporated herein by reference.

[0095] This invention departs from U.S. Pat. No. 5,152,917 (Pieper etal.), however, insofar as the provision of differing dimensioned shapes,among other things, in the array of abrasive composites. This provisocan be established by any convenient approach, e.g., by arbitrarilyassigning at least one-dimensional variance, such as definedhereinbelow, between adjacent composite shapes in a portion or the wholeof the array of composites for an abrasive article. An array of groovescan be formed in a surface of a metal master tool, e.g., by use of adiamond turning machine, from which is produced a production tool havingan array of cavity shapes, which, in turn, can receive and mold anabrasive slurry described herein, which are the inverse shape of thepredetermined array of abrasive composite shapes.

[0096] Alternatively, as described herein, a copy of a desired patternof variably dimensioned shapes of abrasive composites can be formed inthe surface of a so-called metal master, e.g., aluminum, copper, bronze,such as by diamond turning grooves to leave upraised portionscorresponding to the desired predetermined shapes of the abrasivecomposites, and then flexible plastic production tooling can be formed,in general, from the metal master by a method explained in U.S. Pat. No.5,152,917 (Pieper et al). As a result, the plastic production toolinghas a surface which includes indentations having the inverse shape ofthe abrasive composites to be formed therewith. Alternatively, the metalmaster can be manufactured by diamond turning grooves to leave thedesired shapes in a metal surface which is amenable to diamond turning,such as aluminum, copper or bronze, and then nickel plating the groovedsurface to provide the metal master. Exemplary techniques for making thevarying dimensioned abrasive composites will be described in greaterdetail hereinbelow.

[0097] Regarding the construction of the abrasive composites per se,referring to FIG. 1 for illustrative purposes, the abrasive composite 12has a boundary 15. The boundary or boundaries associated with the shaperesult in one abrasive composite being physically separated to someextent from another adjacent abrasive composite. To form an individualabrasive composite, a portion of the boundaries forming the shape of theabrasive composite must be separated from one another. Note that in FIG.1, the base or a portion of the abrasive composite closest to thebacking can abutt with an adjacent abrasive composite. Referring to FIG.2, the abrasive article 20 of the invention comprises a backing 21having a plurality of abrasive composites 22 bonded to the backing. Theabrasive composites comprises a plurality of abrasive particles 23 thatare dispersed in a binder 24. In this aspect of the invention, there areopen spaces 25 between adjacent composites. It is also within the scopeof this invention to have a combination of abrasive composites bonded toa backing in which some of adjacent abrasive composites abutt, whileother adjacent abrasive composites have open spaces between them.

[0098] In some instances, e.g., pyramidal non-cylindrical shapes, theboundaries forming the sides of the shape also are planar. For suchshapes that have multiple planes, there are at least four planes(inclusive of three sides and the bottom or base). The number of planesfor a given shape can vary depending upon the desired geometry, forinstance the number of planes can range from four to over 20. Generally,there are between four to ten planes, preferably between four to sixplanes. These planes intersect to form the desired shape and the anglesat which these planes intersect will determine the shape dimensions.Referring to FIG. 1, the abrasive composite 12 has a boundary 15 whichis planar. The side planes 15A and 15b intersect at an angle γ, withcross-section 15C facing the viewer and is coplanar with the page.

[0099] A key aspect of this invention is that at least one the abrasivecomposites has a different dimension from another abrasive composite inthe array. Preferably, the different dimension is established between atleast one pair of adjacent composites, and even more preferably,established for each and every pair of adjacent composites provided onthe surface of the abrasive article. The terminology of “every pair” ofadjacent composites encompasses an arbitrary consideration of everycomposite on the surface of the abrasive article as paired with itsadjacent composite. In general, at least 10% of the pairs of adjacentcomposites have a different dimension therebetween, preferably at least30%, more preferably at least 50%. Most preferably, substantially 100%of the abrasive composites have a different dimension from itsrespective paired adjacent abrasive composite. The result of thisproviso of different dimensions between abrasive composites, viz.between adjacent pairs of abrasive composites, results in an abrasivearticle that produces a relatively finer surface finish on the workpiecebeing abraded or refined. Since the dimensions of adjacent abrasivecomposites vary, there is a reduced tendency for scribed grooves to beimparted by the abrasive composites into the workpiece surface. Ingeneral, if less than 10% of the pairs of abrasive composites have anadjacent composite that has a different dimension, the effect of theinvention of decreasing scribing while achieving high-cut rates and finefinishes may not be satisfactorily realized. In general, the number ofpairs of adjacent abrasive composites that have different dimensions isselected to minimize or reduce scribing. The percentage of the totalabrasive composites that this number of pairs represents will dependupon several factors such as the workpiece type, abrading interfacepressure, abrasive article rotation speed and other typical abradingconditions.

[0100] It is within the scope of this invention to have some, but neverall, of the abrasive composites present on the surface which haveidentical shapes. However, the abrasive composites having identicalshapes, if present, preferably should not be located directly adjacentto or next to one another in order to fully realize the benefits of theinvention. For instance, two abrasive composites in the abrasive articlemay have shapes defined by same dimensions, but, preferably, the twoabrasive composites should be separated from one another in the array ofcomposites by at least one intervening abrasive composite that differsin a dimension from each.

[0101] There must be at least one dimension associated with at least oneof the abrasive composites that is different from another abrasivecomposite. However, it also is within the scope of this invention thatthere are two or more different dimensions therebetween. Thesedimensions can be varied in a variety of ways, such as by providing adifferent length of an edge at the intersection of two planar surfacesof a shape of a composite; by providing a different angle formed at themeeting edge of two adjacent planar surfaces of a shape of a composite;or by providing different types of geometrical shapes for the abrasivecomposites to provide either a different edge length and/or a differentangle.

[0102] If an edge length is varied to provide the different dimensionfor purposes of the invention, in one embodiment, the length ordimensions of the edges in composites, particularly adjacent composites,each having a pyramidal shape as the geometrical shape and a commonheight of between 25 and 1020 micrometers, generally can differ from atleast about 1 to about 500 micrometers, and more preferably between 5 to250 micrometers. In one embodiment, the length of the at least one edgeof a first composite in the array has a length which varies with respectto the length of any edge of a second composite in a ratio between 10:1to 1:10, not inclusive of 1:1, and preferably as between two adjacentcomposites.

[0103] More generally, the abrasive composite shape of this inventioncan be any convenient shape, but it is preferably a three-dimensionalregular geometric shape such as a cubic, prismatic (e.g., triangular,quadrilateral, hexagonal, etc.), conical, truncated conical (flat top),cylindrical, pyramidal, truncated pyramidal (flat top) and the like. Thegeometrical shape of adjacent abrasive composites can be varied, e.g.,pyramidal next to prismatic, in order to provide the requisitedimensional variance therebetween. In one embodiment of the invention,the shapes of the abrasive composites, e.g., pyramidal, all are providedwith the same total height value, measured from the backing, in a rangeof from about 50 micrometers to about 1020 micrometers.

[0104] A preferred geometrical shape is a pyramid and the pyramid can bea four or five side sided (inclusive of the base) pyramid. In onepreferred embodiment, all composite shapes are pyramidal. Even morepreferably, the dimensional variance is achieved between adjacentpyramidal-shaped composites by varying the angle formed by a sidesurface with the backing in adjacent pyramids. For example, angles α andβ formed by the sides of adjacent pyramidal shaped composites, such asdepicted in FIG. 1, are different angles from each other and each have avalue of between 0° and 90° (i.e., non-inclusive of 0° and 90°).Preferably, the angle α or β formed between a side surface of thepyramidal-shaped composites and an imaginary plane 17 (FIG. 1) extendingnormal to the intersection of the respective side surface and thebacking should be greater than or equal to 8°, but less than or equal to45°. From a practical standpoint, angles less than 8° may release curedcomposite shapes from the production tool with greater difficulty. Onthe other hand, angles greater than 45° may unduly enlarge the spacingbetween adjacent abrasive composites such that insufficient abradingsurfaces are provided over the area of the backing.

[0105] It also is preferable to select angles for α and β wherein eachhave a value between 0° and 90° and which differ in magnitude by atleast about 1°, and more preferably at least about 5°.

[0106] It is also preferred to form pyramidal shapes for the abrasivecomposites where two side surfaces of each pyramid meet at the apex ofeach pyramid to form a material-included angle γ (see FIG. 1) in across-sectional view of the pyramid having a value of greater than orequal to 25° and less than or equal to 90°. The lower value of 25° maybe a practical limit since it can be difficult to form a peak or apexshape for an abrasive composite which is sharp and less than 25° withthe slurry and production tool methodology described herein. To morefully realize the benefits of the invention, this proviso with respectto material-included angle γ should be used together with theabove-mentioned proviso that intervening angles α and β between adjacentcomposites be provided as different and randomly selected between 0° and90° as explained hereinabove.

[0107] Further, in any individual abrasive composite, the angles made bythe various surface planes with the backing do not necessarily have tobe the same for a given composite. For instance in a four sided pyramid(one base and three side surfaces), the angles formed by any of thefirst, second and third side planes with the backing can be differentfrom each other. Naturally, the angle at which the side surfacesintersect with each other will also vary as the angle formed between theside surface and the backing are varied.

[0108] Also, in the embodiment of this invention where the dimensionalvariance between adjacent composites is established by varying sidesurface angles between adjacent abrasive composites, such as angles αand β (FIG. 1), it is preferred that the respective angles chosen foreach of α and β between adjacent composites are not repeated andconstant throughout the array of abrasive composites, which is believedto even further ensure no resonance is created between the workpiece andthe abrasive article. Therefore, it is more desirable to permit andprovide different values for each of α and β between 0° and 90° as oneproceeds from one pair adjacent composites to the next immediate pair ofadjacent composites along either the widthwise or lengthwise directionthe abrasive article (e.g., see FIG. 8). This change in the values of αand β between different sets of adjacent composites in the array can beeffected in any convenient manner, such as by randomly picking thevalues for each of α and β between the range 0° and 90°.

[0109] For example, if α, as the right half angle (FIG. 1), can berandomly selected in the range of between 0° and 90° for an abrasivecomposite in one row of composites, then β, as the left half anglefacing α, is randomly chosen for the adjacent abrasive composite in theadjacent row of composites; and then, as one preceeds to the next pairof adjacent abrasive composites in either the widthwise or lengthwisedirection along the rows of composites in the array, a new β, as lefthalf angle, is randomly selected between 0° and 90° and then a new valuefor α, as the facing right half angle, of the adjacent composite can berandomly selected in the range of 0° to 90°, and so forth throughout thearray. This practice is desirable in order to provide a more uniformdistribution of angles between 0° and 90° throughout the array ofabrasive composites in the article.

[0110] The actual selection of the angles α and β, and γ, throughout thearray of abrasive composites, randomly and subject to the preferredconstraints described herein, can be accomplished in any convenientmanner, for example, by systematic random selections of angle values bydraw within the preferred numerical constraint mentioned herein. Thesesystematic selections for an array, can be facilitated and expedited byusing a common computer, e.g., a desktop computer, using the angleconstraints described herein to delimit the range of angle values fromwhich the computer makes a random choice. Algorithms for selection ofrandom numbers are generally known in the statistical and computerfields, and have been adapted to this aspect of the invention. Forinstance, the well-known linear congruential method for generatingpseudorandom numbers can be applied towards randomly selecting theangles α and β. The application and implementation of random numbergeneration for selecting angles for the side faces of the abrasivecomposite shapes in the present application is exemplified in thecomputer source code described in the APPENDIX attached to related U.S.Pat. No. 5,658,184, incorporated herein by reference.

[0111] In any event, the angle values, once so selected for the abrasivecomposites in the array, can be used to determine and predicate thepattern and shapes of indentations formed by a diamond turning machinein the surface of a metal production tool or production tool, which, inturn, can be used to make the abrasive composite articles of theinvention by methods described herein.

[0112] In some instances it is preferred to have the height andgeometrical shape of all the composites as the same. This height is thedistance of the abrasive composite from the backing to its outermostpoint before the abrasive article is used. If the height and shape areconstant, it is then preferred to have the angle between planes vary.

[0113] In order to achieve a fine surface finish on the workpiece, it isalso preferred that the peaks of the abrasive composites do not align ina column which is parallel to the abrading direction performed in themachine direction. If the abrasive composite peaks align in a columnparallel to the abrading direction, this tends to result in groovesimparted to the workpiece and a coarser surface finish. Thus, it ispreferred that the abrasive composites be offset from one another toprevent this alignment.

[0114] In general there are at least 5 individual abrasive compositesper square centimeter. In some instances, there may be at least about100 individual abrasive composites/square centimeter or higher, and morepreferably, about 2,000 to 10,000 abrasive composites/square centimeter.There is no operational upper limit on the density of the abrasivecomposites; although, from a practical standpoint, at some point it maynot be possible to increase the cavity density and/or formprecisely-shaped cavities in the surface of the production toolingpreferably used to make the array of abrasive composites. In general,this number of abrasive composites result in an abrasive article thathas a relatively high rate of cut, a long life, but also results in arelatively fine surface finish on the workpiece being abraded.Additionally, with this number of abrasive composites there is arelatively low unit force per each abrasive composite. In someinstances, this can result in better, more consistent, breakdown of theabrasive composite.

[0115] Method of Making the Abrasive Article

[0116] Although additional details will be described later herein on themethods of making the abrasive article of the invention, in general, thefirst step in making the abrasive article is to prepare an abrasiveslurry. The abrasive slurry is made by combining together by anysuitable mixing technique the binder precursor, the abrasive particles,and the optional additives. Examples of mixing techniques include lowshear and high shear mixing, with high shear mixing being preferred.Ultrasonic energy may also be utilized in combination with the mixingstep to lower the abrasive slurry viscosity. Typically, the abrasiveparticles are gradually added into the binder precursor. The amount ofair bubbles in the abrasive slurry can be minimized by pulling a vacuumduring the mixing step, for example, by employing conventionalvacuum-assisted methods and equipment.

[0117] In some instances it is preferred to heat, generally in the rangeof 30° C. to 70° C., the abrasive slurry to lower the viscosity. It isimportant the abrasive slurry have a rheology that coats well and inwhich the abrasive particles and other fillers do not settle.

[0118] If a thermosetting binder precursor is employed, the energysource can be thermal energy or radiation energy depending upon thebinder precursor chemistry. If a thermoplastic binder precursor isemployed the thermoplastic is cooled such that it becomes solidified andthe abrasive composite is formed. Other more detailed aspects of themethod(s) to make the abrasive article of the invention will bedescribed hereinbelow.

[0119] Production Tool

[0120] A production tool is important, from both practical andtechnological standpoints, in making an abrasive article of theinvention, especially in view of the relatively small sizes of theabrasive composites. The production tool contains a plurality ofcavities. These cavities are essentially the inverse shape of theabrasive composite desired and are responsible for generating the shapeof the abrasive composites. The dimensions of the cavities are selectedto provide the desired shape and dimensions of the abrasive composites.If the shape or dimensions of the cavities are not properly fabricated,the resulting production tool will not provide the desired dimensionsfor the abrasive composites.

[0121] The cavities can be present in a dot like pattern with spacesbetween adjacent cavities or the cavities can abutt against one another.The cavities butt up against one another to facilitate release of theshaped and cured abrasive slurry. Additionally, the shape of thecavities is selected such that the cross-sectional area of the abrasivecomposite decreases in the direction away from the backing.

[0122] In a more preferred embodiment of the production tool, theproduction tool has two opposing parallel side edges bounding an arrayof cavities so configured to provide differing dimensions in the shapesof adjacent abrasive composites formed therewith by methods describedherein over a distinct segment of length of the abrasive article, ineither a length and/or width direction of the abrasive article, and thenthis predetermined pattern of differing composite shapes can be repeatedat least once more or repeatedly along the length and/or width of theabrasive article, if desired and convenient.

[0123] For example, FIG. 7 is a top view representation of a productiontool 70 that can be used to make an abrasive article of the invention.The side edges 71 of the production tool are parallel to the machinedirection (not shown) of the production tool and are perpendicular tothe transverse width direction of the production tool. Cavities 74 aredelimited by intersecting upraised portions represented by solid lines72 and 73. The production tool has six distinct groups A, B, C, D, E andF of cavities, wherein in each group the cavities are aligned inparallel rows bounded by upraised portions 72, wherein the upraisedportions 72 and 73 are the nondeformed (noncavitated) remainder of thetooling sheet. These groups A-E are arranged head-to-tail along thelength of the tooling, as shown in FIG. 7. The rows of cavities in eachgroup that are aligned most closely with side edges 71 trace imaginarylines extending at non-parallel (nonzero) angles to the machinedirection of the production tool, and which angles differ from group Ato group B to group C, and so forth up to group F. The angles of therows of cavities (and intervening upraised portions 72) made with theside edges 71 should be established as between 0° to 90°. Scribingproblems can arise at either 0° or 90° angles for rows of cavities withthe side edges 71. Preferably, angles of 50 to 85° are selected for theangles of the rows of cavities with the machine direction more assuredlyavoid scribing problems.

[0124] The angles of the rows of cavities preferably alternate betweenclockwise and counterclockwise directionality from group to group, asshown in FIG. 7. The angle formed between rows of cavities and upraisedportions 72 and the side edges 71 can be selected to be the same ordifferent in absolute magnitude from set to set.

[0125] An abrasive article formed with production tool 70 by methodsdescribed herein will have an array of abrasive composites formed in theinverse shape to the surface profile presented by the array of cavitiesin the production tool, such production tool 70. By arranging rows ofcavities at angles in the production tooling by means of arrangementssuch as exemplified in FIG. 7, scribing effects can be minimized in theabrasive article made thereby.

[0126] Alternatively, the cavities in the production tool can bearranged to be laterally offset, i.e., nonaligned, from one another inthe direction advancing parallel to the side edges of the productiontool (nondepicted). That is, this embodiment provides an optional mannerof forming an array of abrasive composites and intervening grooves whichare not arranged in rows which extend parallel to the side edges of theabrasive article. Instead, the abrasive composites are staggered fromeach other and non-aligned when viewed from the front of the abrasivearticle into the direction parallel to the side edges of the abrasivearticle.

[0127] The production tool can be a belt, a sheet, a continuous sheet orweb, a coating roll such as a rotogravure roll, a sleeve mounted on acoating roll, or die. The production tool can be composed of metal,(e.g., nickel), metal alloys (e.g., nickel alloys), plastic (e.g.,polypropylene, an acrylic plastic), or any other conveniently formablematerial. The metal production tool can be fabricated by anyconventional technique such as engraving, hobbing, electroforming,diamond turning, and the like.

[0128] A thermoplastic production tool can be made by replication off ametal master tool. The metal master will have the inverse patterndesired for the production tool. The metal master can be made with thesame basic techniques useful in directly making the production tool,e.g., by diamond turning a metal surface. In the event of use of a metalmaster, a thermoplastic sheet material can be heated and optionallyalong with the metal master such that the thermoplastic material isembossed with the surface pattern presented by the metal master bypressing the two surfaces together. The thermoplastic can also beextruded or cast onto to the metal master and then pressed. Thethermoplastic material is cooled to solidify and produce the productiontool. Examples of preferred thermoplastic production tool materialsinclude polyester, polycarbonates, polyvinyl chloride, polypropylene,polyethylene and combinations thereof Alternatively, a plasticproduction tool can be directly made, without the need of a master byengraving or diamond turning a predetermined array of cavities, whichhave the inverse shape of the abrasive composites desired, into asurface of the plastic sheet. If a thermoplastic production tool isutilized, then care must be taken not to generate excessive heat,particularly during the solidifying step, that may distort thethermoplastic production tool. Other suitable methods of productiontooling and metal masters are discussed in commonly assigned U.S. Pat.No. 5,435,816 (Spurgeon et al.).

[0129] For example, a preferred method of making a polymeric productiontool of the invention of the type depicted in FIG. 7 involves the use ofa nickel-plated metal master configured in a drum form. Several flatsections of nickel-plated master, each about 30 centimeters in length,with the varied shapes of indentations corresponding to the shapesdesired for the abrasive composites are provided in a surface thereof,are produced by diamond turning with the aid of a computer directing thecutting action performed by the diamond turning machine. These sectionsof metal master are welded together head-to-tail, with the grooves ofsection being at a non-zero angle to the grooves of the next adjacentsection. This chain of sections is then fixed to a drum so that thecomposites are continuous around the circumference of the drum. Careshould be taken to minimize any weld seams from distending out frombetween the sections and at the point of joining. The production tool iscast by extruding polymeric resin onto the drum and passing theextrudant between a nip roll and the drum, and then cooling theextrudant to form a production tool in sheet form having an array ofcavities formed on the surface thereof in inverse correspondence to thesurface indentations presented by the master on the drum. This processcan be conducted continuously to produce a polymeric tool of any desiredlength.

[0130] Energy Sources

[0131] When the abrasive slurry comprises a thermosetting binderprecursor, the binder precursor is cured or polymerized. Thispolymerization is generally initiated upon exposure to an energy source.Examples of energy sources include thermal energy and radiation energy.The amount of energy depends upon several factors such as the binderprecursor chemistry, the dimensions of the abrasive slurry, the amountand type of abrasive particles and the amount and type of the optionaladditives. For thermal energy, the temperature can range from about 30°C. to 150° C., generally between 40° C. to 120° C. The time can rangefrom about 5 minutes to over 24 hours. The radiation energy sourcesinclude electron beam, ultraviolet light, or visible light. Electronbeam radiation, which is also known as ionizing radiation, can be usedat an energy level of about 0.1 to about 10 Mrad, preferably at anenergy level of about 1 to about 10 Mrad. Ultraviolet radiation refersto non-particulate radiation having a wavelength within the range ofabout 200 to about 400 manometers, preferably within the range of about250 to 400 manometers. It is preferred that 300 to 600 Watt/inch (120 to240 Watt/cm) ultraviolet lights are used. Visible radiation refers tonon-particulate radiation having a wavelength within the range of about400 to about 800 manometers, preferably in the range of about 400 toabout 550 manometers. It is preferred that 300 to 600 Watt/inch (120 to240 Watt/cm) visible lights are used.

[0132] One method to make the abrasive article of the invention isillustrated in FIG. 3. Backing 41 leaves an unwind station 42 and at thesame time the production tool 46 leaves an unwind station 45. Cavities(not depicted) formed in the upper surface of production tool 46 arecoated and filled with an abrasive slurry by means of coating station44. Alternatively, coating station 44 can be relocated to deposit theslurry on backing 41 instead of the production tool before reaching drum43 and the same ensuing steps are followed as used for coating theproduction tooling as described below. Either way, it is possible toheat the abrasive slurry (not shown) and/or subject the slurry toultrasonics prior to coating to lower the viscosity. The coating stationcan be any conventional coating means such as drop die coater, knifecoater, curtain coater, vacuum die coater or a die coater. Duringcoating the formation of air bubbles should be minimized. The preferredcoating technique uses a vacuum die coater, which can be of the typesuch as described in U.S. Pat. Nos. 3,594,865; 4,959,265 and 5,077,870,which are incorporated herein by reference. After the production tool iscoated, the backing and the abrasive slurry are brought into contact byany means such that the abrasive slurry wets the front surface of thebacking. In FIG. 3, the abrasive slurry is brought into contact with thebacking by means of contact nip roll 47, and contact nip roll 47 forcesthe resulting construction against support drum 43. Next, any convenientform of energy 48 is transmitted into the abrasive slurry that isadequate to at least partially cure the binder precursor. The termpartial cure is meant that the binder precursor is polymerized to such astate that the abrasive slurry does not flow from an inverted test tube.The binder precursor can be fully cured once it is removed from theproduction tool by any energy source. The production tool is rewound onmandrel 49 so that the production tool can be reused again.Additionally, abrasive article 120 is wound on mandrel 121. If thebinder precursor is not fully cured, the binder precursor can then befully cured by either time and/or exposure to an energy source.Additional steps to make the abrasive article according to this firstmethod is further described in U.S. Pat. No. 5,152,917 (Pieper et al.),which is incorporated herein by reference, or commonly assigned U.S.Pat. No. 5,435,816 (Spurgeon et al.). Other guide rolls are used whereconvenient and are designated rolls 40.

[0133] Relative to this first method, it is preferred that the binderprecursor is cured by radiation energy. The radiation energy can betransmitted through the production tool or backing so long as theproduction tool or backing does not appreciably absorb the radiationenergy. Additionally, the radiation energy source should not appreciablydegrade the production tool. It is preferred to use a thermoplasticproduction tool and ultraviolet or visible light.

[0134] As mentioned above, in a variation of this first method, theabrasive slurry can be coated onto the backing and not into the cavitiesof the production tool. The abrasive slurry coated backing is thenbrought into contact with the production tool such that the abrasiveslurry flows into the cavities of the production tool. The remainingsteps to make the abrasive article are the same as detailed above.

[0135] A second method for making the abrasive article is illustrated inFIG. 4. The production tool 55 is provided in the outer surface of adrum, e.g., as a sleeve which is secured around the circumference of adrum in separate sheet form (e.g., as a heat-shrunk nickel form) in anyconvenient manner. Backing 51 leaves an unwind station 52 and theabrasive slurry is coated into the cavities of the production tool 55 bymeans of the coating station 53. The abrasive slurry can be coated ontothe backing by any technique such as drop die coater, roll coater, knifecoater, curtain coater, vacuum die coater, or a die coater. Again, it ispossible to heat the abrasive slurry and/or subject the slurry toultrasonics prior to coating to lower the viscosity. During coating theformation of air bubbles should be minimized. Then, the backing and theproduction tool containing the abrasive slurry are brought into contactby a nip roll 56 such that the abrasive slurry wets the front surface ofthe backing. Next, the binder precursor in the abrasive slurry is atleast partially cured by exposure to an energy source 57.

[0136] After this at least partial cure, the abrasive slurry isconverted to an abrasive composite that is bonded or adhered to thebacking. The resulting abrasive article 59 is stripped and removed fromthe production tool at nip rolls 58 and wound onto a rewind station 60.In this method, the energy source can be thermal energy or radiationenergy. If the energy source is either ultraviolet light or visiblelight, the backing should be transparent to ultraviolet or visiblelight. An example of such a backing is polyester backing. Other guideand contact rolls can be used where convenient and are designated rolls50.

[0137] In another variation of this second method, the abrasive slurrycan be coated directly onto the front surface of the backing by movingcoating station 53 to a location upstream from roll 56. The abrasiveslurry coated backing is then brought into contact with the productiontool such that the abrasive slurry wets into the cavities of theproduction tool. The remaining steps to make the abrasive article arethe same as detailed above.

[0138] After the abrasive article is made, it can be flexed and/orhumidified prior to converting. The abrasive article can be convertedinto any desired form such as a cone, endless belt, sheet, disc, etc.before the abrasive article is put into service.

[0139] Method of Refining a Workpiece Surface

[0140] Another embodiment of this invention pertains to a method ofrefining a workpiece surface. This method involves bringing intofrictional contact the abrasive article of this invention with aworkpiece. The term refine means that a portion of the workpiece isabraded away by the abrasive article. Additionally, the surface finishassociated with the workpiece surface is reduced after this refiningprocess. One typical surface finish measurement is Ra; Ra is thearithmetic surface finish generally measured in microinches ormicrometers. The surface finish can be measured by a profilometer, suchas that available under the trade designation Perthometer or Surtronic.

[0141] Workpiece

[0142] The workpiece can be any type of material such as metal, metalalloy, exotic metal alloy, ceramic, glass, wood, wood like material,composites, painted surface, plastic, reinforced plastic, stone, andcombinations thereof The workpiece may be flat or may have a shape orcontour associated with it. Examples of workpieces include glassophthalmic lenses, plastic ophthalmic lenses, glass television screens,metal automotive components, plastic components, particle board, camshafts, crank shafts, furniture, turbine blades, painted automotivecomponents, magnetic media, and the like.

[0143] Depending upon the application, the force at the abradinginterface can range from about 0.1 kg to over 1000 kg. Generally thisrange is between 1 kg to 500 kg of force at the abrading interface. Alsodepending upon the application, there may be a liquid present duringabrading. This liquid can be water and/or an organic compound. Examplesof typical organic compounds include lubricants, oils, emulsifiedorganic compounds, cutting fluids, soaps, or the like. These liquids mayalso contain other additives such as defoamers, degreasers, corrosioninhibitors, or the like. The abrasive article may oscillate at theabrading interface during use. In some instances, this oscillation mayresult in a finer surface on the workpiece being abraded. An abrasivecomposite having an adjacent abrasive composite with a differentdimension attributes to this relatively fine surface finish. since aportion of the abrasive composites have different dimensions, theabrasive composites may not perfectly align in a row from theperspective of the apices of pyramidal shapes and the like. For example,FIG. 8 includes a representative topographical top view (and side views)of an abrasive article 85 of the invention wherein an abrasive compositetherein is designated 80 having a face 82 and apex 81. As seen in FIG.8, the pyramidal shapes, as a whole, align in rows, and therefore, theapices of the abrasive composites are aligned irrespective of thedifferences in side dimensions between adjacent abrasive compositesfacing each other across common grooves. This arrangement results inscratches imparted into the workpiece by the abrasive composites whichare continuously crossed over. This continuous crossing of previousscratches results, in the aggregate, in the finer surface finish.

[0144] The abrasive article of the invention can be used by hand or usedin combination with a machine. At least one or both of the abrasivearticle and the workpiece is moved relative to the other. The abrasivearticle can be converted into a belt, tape rolls, disc, sheet, and thelike. For belt applications, the two free ends of an abrasive sheet arejoined together and a splice is formed. It is also within the scope ofthis invention to use a spliceless belt. Generally the endless abrasivebelt traverses over at least one idler roll and a platen or contactwheel. The hardness of the platen or contact wheel is adjusted to obtainthe desired rate of cut and workpiece surface finish. The abrasive beltspeed ranges anywhere from about 150 to 5000 meters per minute,generally between 500 to 3000 meters per minute. Again this belt speeddepends upon the desired cut rate and surface finish. The beltdimensions can range from about 5 mm to 1 meter wide and from about 5 cmto 10 meters long. Abrasive tapes are continuous lengths of the abrasivearticle. They can range in width from about 1 mm to 1 meter, generallybetween 5 mm to 25 cm. The abrasive tapes are usually unwound, traverseover a support pad that forces the tape against the workpiece and thenrewound. The abrasive tapes can be continuously feed through theabrading interface and can be indexed. The abrasive disc, which alsoincludes what is known in the abrasive art as “daisies”, can range fromabout 50 mm to 1 meter in diameter. Typically abrasive discs are securedto a back-up pad by an attachment means. These abrasive discs can rotatebetween 100 to 20,000 revolutions per minute, typically between 1,000 to15,000 revolutions per minute.

[0145] The features and advantages of the present invention will befurther illustrated by the following non-limiting examples.

[0146] All parts, percentages, ratios, etc, in the examples are byweight unless otherwise indicated.

Experimental Procedure

[0147] The following abbreviations are used throughout:

[0148] TMPTA: trimethylol propane triacrylate;

[0149] TATHEIC: triacrylate of tris(hydroxy ethyl)isocyanurate;

[0150] PH2: 2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)1-butanone, commercially available from Ciba Geigy Corp. under the tradedesignation IRGACURE 369;

[0151] ASF: amorphous silica filler, commercially available from DeGussaunder the trade designation OX-50;

[0152] FAO: fused heat treated aluminum oxide;

[0153] WAO: white fused aluminum oxide; and

[0154] SCA: silane coupling agent,3-methacryloxypropyltrimethoxy-silane, commercially available from UnionCarbide under the trade designation A-174.

[0155] General Procedure for Making the Abrasive Article

[0156] An abrasive slurry was prepared that contained 20.3 parts TMPTA,8.7 parts TATHEIC, 0.3 parts PH2, 1 part ASF, 1 part SCA and 69 parts ofgrade P-320 FAO. The slurry was mixed for 20 minutes at 1200 rpm using ahigh shear mixer.

[0157] The production tool was a continuous web made from apolypropylene sheet material commercially available from Exxon under thetrade designation POLYPRO 3445. The production tool was embossed off ofa nickel-plated master. The master tool was made by diamond cutting apattern of varying dimension grooves and indentations according to thecomputer programs described in the APPENDIX, and then nickel plated. TheAPPENDIX includes the source code for four computer programs, which, ingeneral, comprises a first program entitled “VARI-l.BAS”, whichgenerated and determined random left and right angles for side surfacesof five sided pyramidal shapes and also the material included angles forthese shapes; the second program entitled “VARI-STAT.BAS” statisticallytallied the number and values of the left, right, and material includedangles in x and y coordinates in the array of shapes to assurerandomness; the third program entitled “TOPVIEW.BAS” took the randomangle file and calculated where the valleys and peaks appear for theshapes having the angles determined by the first program for a squareinch (6.5 cm²) and printed out a display on a computer screen or printerof the topography of the array of shapes; and the fourth program“MAKETAPE.BAS” took the determined angles and generated a code tocontrol the number and type of grooves required to be cut by the diamondturning machine to make a 22.5 inch (57 cm) wide pattern of randomshapes generated by the first program.

[0158] In general, the production tool, as made from the master toolmade using the above-mentioned four programs, contained an array ofcavities that were inverted five sided pyramids (inclusive of the mouthof the cavity as a “base”) that had a constant depth of about 355micrometers but varied in dimension between 8° and 45° for adjacentcavities in terms of the angle made by side faces with the intersectionof a plane extending normal to the plane of tool and the materialincluded angle or apex angle of each composite was at least 25°.

[0159] The abrasive article was made by a method and arrangementgenerally depicted in FIG. 3. This process was a continuous process thatoperated at about 15.25 meters/minute. The backing was a J weight rayonbacking that contained a dried latex/phenolic presize coating to sealthe backing. The abrasive slurry was knife-coated onto a production toolwith a 76 micrometer knife gap (3 mil) and about a 15 cm wide coatingarea onto the production tool. The nip pressure, such as exerted by roll47 in FIG. 3, between the production tool and the backing was about 40pounds. The energy source was one visible-light lamp, which contained aV-bulb made by Fusion Systems, Co., which operated at 600 Watts/inch(240 Watt/cm). After curing the abrasive slurry, the resulting coatedabrasive was thermally cured for 12 hours at 240° F. (116° C.) to finalcure the phenolic presize of the backing.

[0160] Test Procedure I

[0161] The coated abrasive article was converted into 7.6 cm by 335 cmendless belt and tested on a constant load surface grinder. Apre-weighed, 4150 mild steel workpiece approximately 2.5 cm by 5 cm by18 cm was mounted in a holder. The workpiece was positioned vertically,with the 2.5 cm by 18 cm face facing an approximately 36 cm diameter 65Shore A durometer serrated rubber contact wheel with one on one landsover which was entrained the coated abrasive belt. The workpiece wasthen reciprocated vertically through an 18 cm path at the rate of 20cycles per minute, while a spring loaded plunger urged the workpieceagainst the belt with a load of 4.5 kg (10 lbs.) as the belt was drivenat about 2050 meters per minute. After thirty seconds elapsed grindingtime, the workpiece holder assembly was removed and re-weighed, theamount of stock removed calculated by subtracting the abraded weightfrom the original weight, and a new, pre-weighed workpiece and holderwere mounted on the equipment. Additionally, the surface finish (Ra)and, in some cases, the Rtm, of the workpiece was also measured andthese procedures will be described below. The test endpoint was when theamount of steel removed in the thirty second interval was less than onethird the value of the steel removed in the first thirty seconds ofgrinding or until the workpiece burned, i.e., became discolored.

[0162] Test Procedure II

[0163] The same procedure as Test Procedure I was used except that a1018 mild steel workpiece was used.

[0164] Test Procedure III

[0165] A maple dowel rod that had a diameter of approximately 3 cm wasinstalled on a lathe. The dowel rod was rotated at about 3800 rpm. Astrip of abrasive article (1 inch (2.54 cm) wide and 12 inches (30.5 cm)long) was held against the dowel rod without any oscillation forapproximately 15 to 20 seconds. After abrading, the dowel rod wasstained with a cherry oil stain commercially available from Watco.

[0166] Ra is a common measure of roughness used in the abrasivesindustry. Ra is defined as the arithmetic mean of the departures of theroughness profile from the mean line. Ra was measured with aprofilometer probe, which was a diamond tipped stylus. In general, thelower the Ra value was, the smoother or finer the workpiece surfacefinish. The results were recorded in micrometers. The profilometer usedwas a Perthen M4P.

[0167] Rtm is a common measure of roughness used in the abrasiveindustry. Rtm is defined as the mean of five individual roughness depthsof five successive measuring lengths, where an individual roughnessdepth is the vertical distance between the highest and lowest points ina measuring length. Rtm is measured the same as Ra. The results arerecorded in micrometers. In general, the lower the Rtm, the smoother thefinish.

EXAMPLES Examples 1, IA and Comparative Examples A, AA

[0168] Abrasive articles representative of the invention were comparedwith conventional coated abrasive articles having uniformly shaped anddimensioned abrasive composites. Example 1 was made according to the“General Procedure for Making the Abrasive Article” describe herein.Comparative Example A was a grade P3203M 201E Three-M-ite Resin Bondcloth JE-VF coated abrasive commercially available from 3M Company, St.Paul, Minn. These abrasive products were tested according to TestProcedure I and the test results can be found in Table 1. Also,additional Example 1A and Comparative Example AA were performed whereinExample 1 and Comparative Example A were repeated, except that TestProcedure II was used in lieu of Test Procedure I. The results also aresummarized in Table 1. TABLE 1 Run Ex. 1 C. Ex. A Ex. 1A C. Ex. AA Init.Cut (grams) 12.2 15.3 13.3 11.8 Init. Ra (μm) 0.86 0.88 0.98 1.18 Init.Rtm (μm) 9.43 10.66 Total Cut (grams) 283.6 156.8 255.5 247.2 Final Ra(μm) 0.33 0.43 0.37 0.40 Final Rtm (μm) 3.11 3.92

[0169] The above results show that the abrasive articles of the presentinvention, as represented by Examples 1 and 1A, demonstrated higher cutand provided finer finish than the comparison examples using exclusivelyidentically shaped abrasive composites.

Example 2 and Comparative Examples B through E

[0170] This set of examples compared the abrasive article of theinvention with abrasive articles that had only one commonly shaped anddimensioned type of abrasive composite present on the backing. All ofthese examples were made according to “General Procedure for Making theAbrasive Article”, described above, except for the following changes.The abrasive slurry consisted of 20.3 parts TMPTA, 8.7 parts TATHEIC, 1part PH2, 1 part ASF, 1 part SCA, and 69 parts of 40 micrometer WAO.Also, the production tool for comparative Examples B through E was anembossed polypropylene thermoplastic continuous web that contained fivesided pyramidal type cavities (inclusive of the mouth of the cavity as a“base”). The cavities for Comparative Examples B through E were allidentical in dimensions and the cavities butted up against one another.The height of the cavities for Comparative Example B was about 178micrometers, for Comparative Example C was about 63.5 micrometers, forComparative Example D was about 711 micrometers and Comparative ExampleE was about 356 micrometers.

[0171] Example 2 and Comparative Examples B through E then were testedaccording to Test Procedure III above. The stained maple dowel rodabraded with Comparative Examples B through E showed evidence of groovesvisible by the naked eye. In contrast, the stained maple dowel rodabraded with Example 2 representing the present invention showed noevidence of grooves visible by the naked eye and produced a very finefinish on the wood workpiece.

[0172] Various modifications and alterations of this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A master tool for manufacturing a production tooluseful to manufacture an abrasive article that comprises a major surfacehaving deployed in fixed position thereon first and secondthree-dimensional abrasive composites, each of said compositescomprising abrasive particles dispersed in a binder and having a shapedefined by a substantially distinct and discernible boundary whichincludes substantially specific dimensions, wherein said first abrasivecomposite has a first shape having specific first dimensions and saidsecond abrasive composite has a second shape having second specificdimensions, wherein each of said abrasive composites has a boundarydefined by at least four planar surfaces wherein adjacent planarsurfaces of one composite meet at an edge to define an angle ofintersection therebetween, wherein at least one angle of intersection ofsaid first abrasive composite is different from all of the angles ofintersection of said second composite, said master tool comprising astructure having a major surface having a plurality of adjacentthree-dimensional shapes projecting therefrom, wherein eachthree-dimensional shape is defined by a substantially distinct anddiscernible boundary which includes substantially specific dimensions,wherein a first three-dimensional shape has a first shape havingspecific first dimensions and a second three-dimensional shape has asecond shape having second specific dimensions, wherein each of saidthree-dimensional shapes has a boundary defined by at least four planarsurfaces wherein adjacent planar surfaces of one three-dimensional shapemeet at an edge to define an angle of intersection therebetween, whereinat least one angle of intersection of said first three-dimensional shapeis different from all angles of intersection of said secondthree-dimensional shape.
 2. The master tool of claim 1, wherein saidthree-dimensional shapes comprise pyramids.
 3. The master tool of claim2, wherein each said pyramid comprises planar surfaces which intersectto form a material-included angle at a distal end of said pyramid,wherein said material-included angle is a value from 25° and 90°.
 4. Themaster tool of claim 1, comprised of a metal material.
 5. The mastertool of claim 4, wherein said master tool surface is nickel-plated.
 6. Amaster tool for manufacturing a production tool useful to shape anabrasive slurry into an array of three-dimensional nonidentical abrasivecomposites, said master tool having a major surface extending within afirst imaginary plane, said master tool being made by a methodcomprising the steps of: (1) determining angles corresponding to facingright and left planar surfaces of adjacent three-dimensional shapes andwherein each of said angles has a value as measured between its planarsurface and a plane which extends in a normal direction to said majorsurface and contains an edge of said planar surface in contact with saidmajor surface, by the following substeps: (i) selecting an angle valuebetween, but not including, 0° and 90° to establish a first right halfangle of a first right planar surface of a first right-sidethree-dimensional shape with a random number generating means capable ofrandomly selecting an angle value between, but not including, 0° and90°; (ii) selecting an angle value between, but not including, 0° and90° with said random number generating means to establish a first lefthalf angle for a first left planar surface of a first left-sidethree-dimensional shape facing said first right planar surface of saidfirst right-side three-dimensional shape; (iii) proceeding along a firstdirection extending linearly within said first imaginary plane to asecond left planar surface of a second left-side three-dimensional shapelocated adjacent said first left-side three-dimensional shape and usingsaid random number generating means to select a value between, but notincluding, 0° and 90° to establish a second left planar angle for saidsecond left planar surface; (iv) using said random number generatingmeans to select a value between, but not including, 0° and 90° for asecond right planar surface of a second right-side three-dimensionalshape facing said second left planar surface; (v) proceeding along saidfirst direction to a third right-side three-dimensional shape locatedadjacent said second right-side three-dimensional shape; (vi) repeatingsaid substeps (i), (ii), (iii), (iv), and (v), in that sequence, atleast once; (2) repeating step (1) except that the angles are determinedfor left and right planar surfaces of adjacent three-dimensional shapesdeployed in two adjacent rows in a second direction extending linearlywithin said first imaginary plane, wherein said first and seconddirections intersect; (3) using means to determine, for a given width ofsaid surface of said master, locations of grooves required to be cut bya cutting means to form a series of intersecting grooves defining aplurality of three-dimensional shapes having said angles calculated bysteps (1) and (2); and (4) providing a cutting means to cut grooves insaid surface of said master in correspondence to said angles calculatedby steps (1) and (2) and said groove locations determined by step (3) toform a series of intersecting grooves which define a plurality ofthree-dimensional shapes upraised from said surface, each of said shapesbeing defined by a distinct and discernible boundary including specificdimensions, wherein not all said three-dimensional shapes are identical.7. The master tool of claim 6, wherein said right and left half angleseach have a value between 8° and 45°.
 8. The master tool of claim 6,wherein said three-dimensional shapes comprise pyramids.
 9. The mastertool of claim 6, wherein each said pyramid comprises planar surfaceswhich intersect to form a material-included angle at a distal end ofsaid pyramid, wherein said material-included angle is a value from 25°and 90°.
 10. The master tool of claim 6, wherein said cutting meanscomprises a diamond cutting tool.
 11. The master tool of claim 6,comprised of a metal material.
 12. The master tool of claim 6 whereinsaid major surface is nickel-plated after completing said step (4). 13.The master tool of claim 6, wherein said first and said seconddirections are oriented perpendicular to each other.
 14. A productiontool for manufacturing an abrasive article that comprises a majorsurface having deployed in fixed position thereon first and secondthree-dimensional abrasive composites, each of said compositescomprising abrasive particles dispersed in a binder and having a shapedefined by a substantially distinct and discernible boundary whichincludes substantially specific dimensions, wherein said first abrasivecomposite has a shape having specific first dimensions and said secondabrasive composite has a second shape having second specific dimensions,wherein each of said abrasive composites has a boundary defined by atleast four planar surfaces wherein adjacent planar surfaces of onecomposite meet at an edge to define an angle of intersectiontherebetween, wherein at least one angle of intersection of said firstabrasive composite is different from all of the angles of intersectionof said second composite, said production tool comprising a structurehaving a plurality of adjacent three-dimensional cavities form on amajor surface thereof, wherein each three-dimensional cavity is definedby a substantially distinct and discernible boundary which includessubstantially specific dimensions, wherein a first three-dimensionalcavity has a first shape having specific first dimensions and a secondthree-dimensional cavity has a second shape having second specificdimensions, wherein each of said three-dimensional cavities has aboundary defined by at least four planar surfaces wherein adjacentplanar surfaces of one three-dimensional cavity meet at an edge todefine an angle of intersection therebetween, wherein at least one angleof intersection of said first three-dimensional cavity is different fromall angles of intersection of said second three-dimensional cavity. 15.The production tool of claim 14, wherein said three-dimensional cavitiescomprise geometrical shapes.
 16. The production tool of claim 14,wherein said geometrical shapes are selected from the group ofgeometrical shapes consisting of cubic, prigmatic, pyramidal andtruncated pyramidal shapes.
 17. The production tool of claim 16, whereineach said pyramidal shape comprises planar surfaces which intersect toform a material-included angle at a distal end of said pyramid, whereinsaid material-included angle is a value from 250 and 90°.
 18. Theproduction tool of claim 14, comprised of a material selected from thegroup consisting of metal, metal alloy and plastic.
 19. A productiontool useful to shape an abrasive slurry into an array ofthree-dimensional nonidentical abrasive composites, said production toolmanufactured from a master tool, said master tool being made by a methodcomprising the steps of: (1) determining angles corresponding to facingright and left planar surfaces of adjacent three-dimensional shapes andwherein each of said angles has a value as measured between its planarsurface and a plane which extends in a normal direction to said majorsurface and contains an edge of said planar surface in contact with saidmajor surface, by the following substeps: (i) selecting an angle valuebetween, but not including, 0° and 90° to establish a first right halfangle of a first right planar surface of a first right-sidethree-dimensional shape with a random number generating means capable ofrandomly selecting an angle value between, but not including, 0° and90°; (ii) selecting an angle value between, but not including, 0° and90° with said random number generating means to establish a first lefthalf angle for a first left planar surface of a first left-sidethree-dimensional shape facing said first right planar surface of saidfirst right-side three-dimensional shape; (iii) proceeding along a firstdirection extending linearly within said first imaginary plane to asecond left planar surface of a second left-side three-dimensional shapelocated adjacent said first left-side three-dimensional shape and usingsaid random number generating means to select a value between, but notincluding, 0° and 90° to establish a second left planar angle for saidsecond left planar surface; (iv) using said random number generatingmeans to select a value between, but not including, 0° and 90° for asecond right planar surface of a second right-side three-dimensionalshape facing said second left planar surface; (v) proceeding along saidfirst direction to a third right-side three-dimensional shape locatedadjacent said second right-side three-dimensional shape; (vi) repeatingsaid substeps (i), (ii), (iii), (iv), and (v), in that sequence, atleast once; (2) repeating step (1) except that the angles are determinedfor left and right planar surfaces of adjacent three-dimensional shapesdeployed in two adjacent rows in a second direction extending linearlywithin said first imaginary plane, wherein said first and seconddirections intersect; (3) using means to determine, for a given width ofsaid surface of said master, locations of grooves required to be cut bya cutting means to form a series of intersecting grooves defining aplurality of three-dimensional shapes having said angles calculated bysteps (1) and (2); and (4) providing a cutting means to cut grooves insaid surface of said master in correspondence to said angles calculatedby steps (1) and (2) and said groove locations determined by step (3) toform a series of intersecting grooves which define a plurality ofthree-dimensional shapes upraised from said surface, each of said shapesbeing defined by a distinct and discernible boundary including specificdimensions, wherein not all said three-dimensional shapes are identical.20. The production tool of claim 14 comprising a roll.
 21. Theproduction tool of claim 20 comprising a coating roll.